<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button onclick="alert(123)">按钮</button>

  <script>
    // alert(456)

    //  尽量不要使用多行注释

    //  var a = /[a-z]*/ig
  </script>

  <script src="./02-test.js"></script>
  <!-- 1. 行内 2. script 标签内 3. 导入 -->
</body>
</html>